I want to wash the seat and it looks detachable except for above the mesh section which attaches to the handle bars, these look like rivets. Is there a way to detach the seat from the handlebars?
The Mothercare XSS is actually a made-for Mothercare version of the GB Pockit in different colors. That is why I enclose a fabric removal video of the GB Pockit, as that is easier to find. You'll see how to remove the textiles of your Mothercare XSS around 2:52.
Also, here's a GB Pockit+ (Plus) Stroller Workshop fabrics removal video to consult as this one is more comprehensive and in detail, and the system is pretty much the same. The 'rivets' are actually only studs.
P.S. Watch out for normal machine-washing with your stroller. Do consider the gentlest/hand wash program for sure or a proper handwash /hand cleaning of your stroller. Here is our in-depth stroller cleaning and maintenance guide to explain why to be careful as not to damage your pushchair, and also how to do it properly.